“Mineral grain size” of the valuable mineral is to be understood as referring not to the grain size of the crystallites of said mineral, but to the local spatial extent of the phase of valuable material in the rock.
The mineral grain size and distribution of minerals in a rock has hitherto been time-consumingly determined by taking rock samples at different locations in a deposit or an occurrence and analyzing them. For this purpose, for example, approximately fist-sized lumps of rock are collected and/or exploratory drilling is carried out in a coarse grid pattern in order to obtain evaluatable cores. These rock samples are analyzed in the laboratory in respect of their mineralogical and chemical composition. While the chemical analysis essentially determines the nature and extent of the constituent elements, in the mineralogical analysis the nature and extent of the constituent minerals as well as their spatial arrangement is ascertained. To determine the spatial arrangement of the minerals, the rock samples are ground in the direction of defined spatial axes. By means of optical analysis of the thin or polished section obtained, e.g. under a microscope, the spatial arrangement and distribution of the minerals in the rock can be identified. A spatially widely distributed arrangement of the minerals is associated with a small mineral grain size, while clustering of minerals at particular locations is associated with a larger mineral grain size.
In respect of the structure of a deposit or an occurrence or more specifically the spatial size distribution of the mineral grains in the deposit or occurrence, only a small amount of information can be provided in this way, and this only after a considerable time delay.
Because of this paucity of information, deposit modeling, i.e. creating a model of the deposit or occurrence comprising the three-dimensional plotting of rock layers or rock formations having different grain sizes of the valuable mineral, is virtually impossible. Extraction geared to the locally present rock, i.e. its valuable mineral content and the mineral grain size thereof, and selective utilization is therefore possible only to a limited extent.
Depending on the grain size of the minerals, different size reduction ratios may be required in order to be able to expose the valuable mineral and efficiently separate it from the entire extracted material throughput. Thus, to expose the valuable mineral, a rock including valuable minerals having a high mineral grain size needs to be less intensively comminuted than a rock including valuable minerals having a lower mineral grain size.
The extracted rock has hitherto been comminuted to an average mineral grain size, wherein a first portion of the rock including a valuable mineral having a high mineral grain size is unnecessarily finely comminuted, and a second portion of the rock including a valuable mineral having a lower mineral grain size is insufficiently comminuted. The unnecessarily fine comminution of the first portion of the rock results in an unnecessarily high energy consumption for the comminution process. On the other hand, the insufficient comminution of the second portion of the rock results in inadequate exposing and consequently inadequate separability of the valuable mineral and ineffective exploitation of the deposit.
WO 2010/000055 A1 discloses a method and an apparatus for in particular continuous on-site analysis of drill cuttings from drilling mud. A drill cutting sample which is representative of the drilled rock formation is taken and analyzed in respect of the type of rock and the chemical composition. If necessary, drilling parameters including drilling depth, gamma ray emissions and/or other parameters are logged and correlated with the sample analysis results.